Synodontis melanostictus Boulenger, 1906

Englmaier, Gernot K., Blažek, Radim, Zimmermann, Holger, Bartáková, Veronika, Polačik, Matej, Žák, Jakub, Mulokozi, Deogratias P., Katongo, Cyprian, Büscher, Heinz H., Mabo, Lwabanya, Koblmüller, Stephan, Palandačić, Anja & Reichard, Martin, 2024, Revised taxonomy of Synodontis catfishes (Siluriformes: Mochokidae) from the Lake Tanganyika basin reveals lower species diversity than expected, Zoological Journal of the Linnean Society 202 (3) : -

Synodontis melanostictus Boulenger, 1906

( Fig. 14; Supporting Information, Fig. S10) Synodontis melanostictus Boulenger, 1906: 553 ( Boulenger 1906a) (type locality: Lofu , Lake Tanganyika, Zambia).

Material examined: Type material: BMNH 1906.9 .8.72, holotype, S. melanostictus , 237.0 mm SL, Lofu, Lake Tanganyika , Zambia, coll. Cunnington.

Non-type material: MRAC 1996.083 .P.0002, one, 197.0 mm SL, Lufubu river , lower course, beginning of Yendwe valley escarpment, Lake Tanganyika basin, Zambia, coll. De Vos , 1995. MRAC 126293-126294 , two, 118.4–131.1 mm SL, Uvira , Lake Tanganyika, Democratic Republic of the Congo, coll. Leleup , 1958. MRAC 100515–100517 , three, 171.1–181.2 mm SL, Petite Ruzizi , Burundi, coll. Marlier, Leleup , 1955. MRAC 100518 , one, 136.4 mm SL, Petite Ruzizi , Burundi, coll. Marlier, Leleup , 1955. MRAC 2011.003 .P.1902, one, 89.4 mm SL, Riv. Malagarazi , colline Ngomante, sous-colline Kumana, passerelle Muremera, Burundi, coll. Banyankimbona , 2010. MRAC 2011.003 .P.1901, one, 155.0 mm SL, Riv. Malagarazi , colline Ngomante, sous-colline Kumana, passerelle Muremera, Burundi, coll. Banyankimbona , 2010. MRAC 2010.003 .P.0427, one, 182.1 mm SL, Riv. Malagarazi , Mutwana, parcelle Nyabantu, ± 1000 m vers l’amont, ku kigazo kwa Nyamwikinga, Burundi, coll. Banyankimbona , 2009. NMW 100724 , one, 121.0 mm SL, Ndole Bay (8°28 ʹ 35.1″S, 30°26 ʹ 59.7″E), Lake Tanganyika, Zambia, coll. Reichard, Zimmermann, Polačik, Bartáková , 2021. NMW 100725 , nine, 113.3–173.0 mm SL, Kalambo River at Chipwa (fishermen) (8°35 ʹ 52.34″S, 31°11 ʹ 2.96″E), Zambia, coll. Reichard, Blažek, Zimmermann, Bartáková , 2022. NMW 100726 , four, 95.9–129.1 mm SL (and one C&S specimen in a separate jar, 85.8 mm SL, NMW 100785 ), Kalambo Falls Lodge (8°37 ʹ 24.9″S, 31°11 ʹ 59.5″E), Lake Tanganyika, Zambia, coll. Blažek, Zimmermann, Bartáková, Polačik, Koch , 2022.

Diagnosis: Synodontis melanostictus is distinguished from congeners in the LT basin by a unique combination of characters: axillary pore absent; no granular papillae on head, body, and fins; dorsal spine unpigmented, only its flexible tip pigmented and black; anal fin with abundant brown spots; 23–38 (median 31) mandibular teeth, commonly arranged in four symmetric rows of replacement teeth; 34–64 (median 46) primary premaxillary teeth; 4–7 (median 6) secondary branches on inner mandibular barbels; and 41–44 (median 42) total vertebrae, with 22–24 (median 23) caudal vertebrae.

Description: The general appearance of S. melanostictus is shown in Figure 14 and Supporting Information, Figure S10; axial skeletons in Supporting Information, Figure S8O, P; and relative measurements, meristic counts, and coded characters are given in Supporting Information, Table S12.

Longest examined specimen 237.0 mm SL (undetermined sex, BMNH 1906.9.8.72, holotype). Body slender, moderately compressed laterally. Dorsal head profile and predorsal back rising straight to dorsal-fin origin at an angle of 21° (against midline of body). Postdorsal profile falling straight or slightly concave to adipose fin origin and slightly convex to caudal-fin origin. Body depth at anal-fin insertion slightly shorter than body depth at dorsal-fin origin. Head dorsoventrally compressed; depth at posterior eye margin usually smaller than maximal cranium width. Snout usually longer than half of head length. Mouth subterminal, with abundant papillae on lips; width 72.1%–91.6% of snout length. Eye diameter usually one-third of snout length.

Abundant non-granular papillae on head, extending on body and fins. Thick layer of mucus covering skin in first two-thirds of body on lateral side. Occipitonuchal shield and humeral process deeply rugose and of granular texture. Humeral process broad and triangular in shape, upper margin usually concave; maximal depth 31.7%–44.7% (N = 5) of its length. Axillary pore absent.

Adipose fin well demarcated, its highest point usually above dorsal-fin origin; basal length 27.8%–34.5% SL, extending over 55.2%–68.8% of distance between dorsal-fin insertion and end of caudal peduncle. Adipose-fin insertion close to end of caudal peduncle. Dorsal fin with two unbranched and seven branched rays; dorsal spine densely serrated on lower anterior edge, poorly marked serrations on upper anterior edge, posterior edge with 9–12 serrae; length of dorsal spine, excluding upper flexible part, 79.2%–100.0% of head length. Anal fin with five unbranched rays and eight or nine branched rays; longest rays reaching beyond level of posterior edge of adipose fin. Pelvic fin with a single unbranched ray and six branched rays. Pectoral fin with a single unbranched ray and commonly nine branched rays; pectoral spine densely serrated on anterior (30–45 serrae) and posterior (13–24 serrae) edges. Pectoral fin longer than pectoral–pelvic distance and reaching above pelvic-fin origin in folded position. Caudal fin forked, with 2 + 15 principal rays; number of upper procurrent rays (10– 12, median 11, N = 6) less than lower procurrent rays (10–13, median 13, N = 5).

Mandibular teeth 23–38 (median 31, N = 25) (holotype 28), unicuspid, arranged in four or six symmetric rows of replacement teeth. Primary premaxillary teeth 34–64 (median 46, N = 46) (holotype 62), arranged in two or three irregular rows.

Maxillary barbels long, reaching beyond pectoral-fin insertion. Outer mandibular barbels 48.0%–104.8% of head length, with 5–11 (median 8, N = 26) primary branches; secondary branches absent. Inner mandibular barbels with 9–12 (median 10, N = 26) primary branches and 4–7 (median 6, N = 26) secondary branches.

Lateral-linecanalsossified,extendingbeyondposteriormargin of last complex centrum. One specimen (NMW 100785) with 87 ossified canals. Frontal fontanel (examined in one specimen, 85.8 mm SL, NMW 100785) originating at centre between eyes and extending beyond posterior margin of mesethmoid; shape oval and narrow, anterior and posterior margins rounded; length shorter than interorbital distance between frontal margins; resembling state B in the paper by Pinton (2008: fig. 15).

Total vertebrae 41–44 (median 42, N = 26) (holotype 42), abdominal vertebrae 19–20 (median 19), preanal caudal vertebrae 2–4 (median 3), and postanal caudal vertebrae 19–21 (median 20).

Length of digestive tract (not stretched) ~136%–174% (mean 151%) of SL (N = 4, 95.9– 12.9 mm SL).

Coloration: In life (Supporting Information, Fig. S10), body coloration usually brownish grey, sometimes yellowish. Head, body, and fins covered with abundant black or dark brown spots of variable size/shape; spots smallest and most dense on head, less abundant or absent on ventral side. Smaller specimens with larger and less numerous spots. Dorsal spine unpigmented, only its flexible tip pigmented and black. Maxillary and mandibular barbels usually unpigmented, base of maxillary barbels pigmented and darker.

In formalin (initial fixation) and later transferred to 75% ethanol ( Fig. 14A), body and fins dark brown, greyish, or light cream in colour. Spots dark brown or grey. Maxillary and mandibular barbels cream coloured.

After long-term preservation in 75% ethanol ( Fig. 14B), historical specimens brown or cream in colour, lighter on ventral side; brown spots visible on head, dorsal and lateral side of body, and fins.

Distribution and habitat: Endemic to the basin of LT ( Fig. 1), where it is reported from the lower reaches of tributaries (e.g. Petite Rusizi, Malagarasi, Kalambo, and Lufubu) and the littoral zone of the lake. Uncertain occurrence in Lake Mweru Wantipa. We observed S. melanostictus in the littoral zone near aquatic macrophytes over sandy or muddy bottom. The species seems to be nocturnal and might be most abundant in river estuaries.